Crystal Growth Kinetics of GeSe₂ Polymorphs in Bulk Glasses and Thin Films: Role of Self-Diffusion and Viscosity

The knowledge of transport properties (viscosity and self-diffusion) and the knowledge of crystal growth of different polymorphs in amorphous materials prepared in different forms provide important information for the preparation, processing, and utilization of these materials. This article is the first study of the direct observation of crystal growth rates in amorphous GeSe2 bulk samples and thin films. The study contains a detailed analysis of viscosity and crystal growth in amorphous GeSe2 samples (bulks and thin films), revealing also information about the self-diffusion process. Two polymorphs of GeSe2 crystals (low temperature─LT, and high temperature─HT) grew in GeSe2 bulk glasses. In the thermal evaporated film, only LT-GeSe2 was found. Nevertheless, the crystals in thin films grew far below the glass transition temperature. To properly analyze and describe the crystal growth kinetics, viscosity data were obtained using a thermomechanical analyzer and a nanoindentation system. A combination of crystal growth data and viscosities provides information about the size and transport speed (self-diffusion) of structural units incorporated into the GeSe2 crystals.